1. Field of the Invention
The invention relates to grommets, in particular, to the type of grommet used to seal the entry of wires, cables, optical fibres or the like into the body of a connector used to join them to other similar wires, cables, or fibres.
2. Description of the Prior Art
There are in existence a large number of such connectors in which each part of the connector consists in essence of a hollow connector shell, housing at its forward end a block of dielectric or other material in which are formed a number of longitudinally-extending bores. The electrical contact members or optical fibre terminating members are supported and retained in these bores. At the rear of the connector shell, where the wires or fibres secured to the contact or terminating members enter it, they pass through a grommet of plastics or rubber. The grommet is sealed to the interior of the connector shell around its outer periphery and has a number of openings formed in it which are aligned with the bores at the forward end of the connector. The cables or fibres pass through these openings, each of which is provided with at least one inwardly-directed V-section sealing lip which engages the cable or fibre to seal the interior of the connector against the entry of dirt or moisture. One such connector is described, for example, in United Kingdom Patent No. 1 563 077.
In connectors of this kind it is usual for the contact or terminating members to be permanently secured to the ends of the cables or fibres, the connectors being constructed so that the cables and their attached terminating members can be inserted into or removed from the connector shell at will. It is, therefore, necessary that the grommet should be sufficiently resilient to permit entry of a terminating member whose external diameter is considerably larger than that of the attached cable whilst still forming an adequate seal against the outside of the relatively small diameter cable. Although existing grommets can fulfil both these functions where the diameter of the terminating member is not much greater than that of the cable, an adequate seal is not formed in cases where the cable diameter and the diameter of the terminating member differ greatly.
One existing solution to this problem involves the use of a two-part grommet. The grommet part sealed to the connector shell is similar in form to conventional one-part grommets except that the openings formed in it are sufficiently large to enable the terminating members to pass freely through them into the connector shell. The second part of the grommet in the form of a sleeve or "boot" is threaded on the cable to the rear of the terminating member so that it can be slid into the opening in the main grommet part to fill the space around the cable and seal the interior of the connector shell against dirt and moisture.
Whilst two-part grommets of this kind are satisfactory for many applications, they are more expensive to manufacture than one-part grommets and they have the disadvantage that the sleeve or "boot" must be threaded onto the cable before the terminating member is fitted. In addition, in the case of connectors for use in military or aerospace applicators, it is desirable that the connectors can be serviced in a wide variety of situations. The necessity for a sleeve or boot which can be detached from the connector and lost relatively easily is, therefore, clearly disadvantageous in connectors for use in applications of this kind.